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Home , Gametophyte, Heterospory, Pollen

Chapter 30: Diversity II – The of

1. General Features of Seed-Bearing Plants 2. Survey of the Plant Kingdom II A. B. Angiosperms The 10 Phyla of Existing Plants

Chapter 29

Chapter 30 1. General Features of Seed-bearing Plants Key Adaptations for Life on Land

Plant life on land is dominated by seed plants due to the following 5 derived characters:

1. 2. REDUCED 3. 4. 5. Advantages of Seeds

A seed is a surrounded by nutrients packaged in a protective seed coat which provides the following advantages for the embryo:

• the surrounding the seed can facilitate its dispersal over long distances

• the embryo can survive for years in a dormant state until conditions are favorable for Fireweed seed • nutrients to sustain the embryo during early growth Advantages of Reduced Gametophytes Seed plants have microscopic gametophytes that are fully contained within the of the sporophyte. This provides the following advantages: • the reproductive tissues of the sporangium protect the from environmental stresses (e.g., UV exposure, loss of moisture, extreme temperature)

• the sporophyte can provide nourishment to sustain the gametophyte PLANT GROUP and and other other seedless Seed plants (gymnosperms and angiosperms) nonvascular plants vascular plants Reduced, Independent Reduced (usually microscopic), dependent on Gametophyte Dominant (photosynthetic surrounding sporophyte for nutrition and free-living) Reduced, dependent Sporophyte on gametophyte for Dominant Dominant nutrition Angiosperm

Sporophyte Microscopic (2n) gametophytes (n) Microscopic female inside ovulate cone Sporophyte gametophytes (n) (2n) inside these parts of

Gametophyte Microscopic (n) male Example gametophytes (n) inside these parts Microscopic of flowers male gametophytes (n) inside pollen cone Sporophyte (2n) Sporophyte (2n) Gametophyte (n) Advantages of Heterospory Most seedless plants are homosporous – produce one type of that develops into a bisexual gametophyte. Seed plants are heterosporous and produce 2 types of :

Megasporangium Female on megasporophyll gametophyte Microsporangium Male on microsporophyll gametophyte This provides 2 key advantages: 1. male & female gametophytes can mature at different times avoiding self fertilization and increasing genetic diversity 2. a separate female gametophyte can better support a developing embryo Production in Ovules Seed plants are unique in containing the megasporangium within the parent sporophyte surrounded by a protective integument.

Immature The complete ovulate cone structure – Integument (2n) Female Seed coat megaspore within gametophyte (n) Megaspore (n) megasporangium Spore Spore wall Egg nucleus wall within the (n) integument – is Discharged called an . Megasporangium sperm nucleus supply (2n) (n) (n) Pollen Male Embryo (2n) Micropyle grain (n) gametophyte (n)

(a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed Pollen and Sperm Production develop into multicellular pollen grains – a male gametophyte surrounded by a protective outer layer containing produced by the sporophyte.

• pollen grains protect the male – sperm – and facilitate their dispersal without the requirement for water

• unlike seedless plants, the sperm contained in pollen grain are not flagellated and gain access to an egg at through a pollen tube Five Derived Traits of Seed Plants

Reduced Microscopic male and Male Summary of the Key gametophytes female gametophytes gametophyte (n) are nourished and protected by the Female Derived Traits of sporophyte (2n) gametophyte

Heterospory Microspore (gives rise to a male gametophyte) Seed Plants

Megaspore (gives rise to a female gametophyte)

Ovules Integument (2n) Ovule (gymnosperm) Megaspore (n) Megasporangium (2n)

Pollen Pollen grains make water unnecessary for fertilization

Seeds Seeds: survive Seed coat better than unprotected spores, can be Food supply transported long distances Embryo 2A. Survey of the Plant Kingdom II Gymnosperms

Nonvascular plants ()

Seedless vascular plants

Gymnosperms Angiosperms Gymnosperm Characteristics Gymnosperms are at least 300 million years old according to the record and were the dominant group of land plants in the Mesozoic era, with many still existing today.

• gymnosperm means “naked seed” which refers to the exposed seeds produced on modified () of cones • cones are a type of , a collection of sporophylls

It takes approximately 3 years for an ovulate cone to produce mature seeds! Ovule The Life Cycle

Megasporocyte (2n) Ovulate cone of a Integument Pollen cone Microsporocytes Pollen Megasporangium Mature (2n) grains (n) sporophyte (2n) • most such as (2n) Germinating MEIOSIS produce both pollen grain ovulate (female) Seedling Microsporangium (2n) cones and pollen Surviving (male) cones megaspore (n) Seeds Female gametophyte • pollen grains Food Sperm have an aerodynamic reserves Seed nucleus (n) coat (2n) morphology and reach Pollen tube Key megasporangia Embryo Haploid (n) (new sporophyte) FERTILIZATION Diploid (2n) through the air (2n) Egg nucleus (n) Gymnosperm Phyla

4 of the 10 plant phyla are gymnosperms:

• CYCADOPHYTA • GINGKOPHYTA • • CONIFEROPHYTA Phylum Cycadophyta

Cycads have large cones and palm-like leaves.

• produce flagellated sperm unlike most seed plants

• widespread during the Mesozoic period, most modern species are endangered

Cycas revoluta Phylum Ginkgophyta

There is only one living species in this phylum: Gingko biloba

• produces flagellated sperm like the

• a popular ornamental in southern California

Ginkgo biloba Phylum Gnetophyta

This phylum contains only 3 genera: Gnetum, Ephedra, and Welwitschia Welwitschia Gnetum

Ovulate cones • some species are tropical and others thrive in deserts

Welwitschia Ephedra Phylum Coniferophyta

• this is the largest gymnosperm phylum with ~600 known species • most conifers are evergreens Douglas that carry out year round

Bristlecone pine Common juniper Sequoia European larch 2B. Survey of the Plant Kingdom Angiosperms

Nonvascular plants (bryophytes)

Seedless vascular plants

Gymnosperms Angiosperms Characteristics of Angiosperms

All angiosperms (literally “enclosed seeds”) or flowering plants belong to the phylum Anthophyta and have 2 key adaptations:

1. Flowers as sexual reproductive structures

2. Seeds enclosed in which aid in Flowers Carpel Anther Style Flowers are modified Filament containing up to 4 types of modified leaves:

• that enclose and protect the • to attract • – the male reproductive organs Ovule • carpels – the female reproductive organs Variations in Flower Structure Location of Stamens Flower Symmetry and Carpels • flowers of any given Sepal Common species of angiosperm holly Radial flowers may have radial or symmetry with bilateral symmetry (daffodil) stamens

Fused petals Stamens • flowers of any given

Nonfunctional species may also be Carpel stamen complete (have all 4 Bilateral flower organs) or symmetry (orchid) Common incomplete (lacking at holly flowers least one flower organ with carpels Fruits develop from Fruits

the ovary wall and ▼ Mechanisms that aid in the dispersal disperse seeds by of seeds by a variety ▼ explosive action of methods: ▼ Ruby grapefruit

• animals disperse ▼ Wings seeds in edible fruits ▼ Nectarine • wind disperses some

seeds (e.g., dandelion) ▼ Seeds within • hitchhiker fruits act and as barbs to stick to other edible ▼ animals passersby Hazelnut fruits • some fruits burst open when dry to disperse seeds

▼ Barbs ▼ • (e.g., peas) Milkweed Microsporangium Carpel Anther Microsporocytes (2n) Mature flower on Angiosperm sporophyte plant Microspore (2n) MEIOSIS (n) Generative cell Ovule with Tube cell Life Cycle megasporangium (2n) Tube nucleus Male gametophyte (in pollen grain) Ovary (n) Germinating MEIOSIS Pollen grains seed Stigma Pollen tube Megasporangium Surviving (2n) Sperm Embryo (2n) megaspore Integuments (n) Tube (3n) Seed Micropyle nucleus Seed coat (2n) Antipodal cells Polar nuclei Style Female in central cell gametophyte (embryo sac) Synergids Egg (n) (2n) Nucleus of developing Egg endosperm nucleus (n) (3n) FERTILIZATION Key Haploid (n) Discharged sperm nuclei (n) Diploid (2n) Carpel Possible Angiosperm floats Stamen History

• the oldest angiosperm fossil dates to ~140 million years ago 5 cm (a) Archaefructus sinensis, • angiosperms a 125-million-year-old fossil dominate the fossil record as of ~100

(b) Artist’s reconstruction of million years ago Archaefructus sinensis and still dominate the world today Evolutionary Links with Animals Many animals and angiosperms have coevolved due to close relationships that may be adversarial or mutually beneficial:

• angiosperms have evolved defenses in response to that would eat them • angiosperms and their animal pollinators have evolved characters to reinforce their mutualistic symbioses Angiosperm Phylogeny

Living gymnosperms

MicrosporangiaFossil and Bennettitales (contain microspores)molecular

evidence Water lilies dictate the Most recent common Star anise and ancestor of all living relatives angiosperms evolutionary

history Monocots Ovules shown here.

300 250 200 150 100 50 0 (a) A close relative of the angiosperms? Millions of years ago Angiosperm Diversity

Angiosperms used to be divided into 2 groups – monocots & dicots – however now there are 6 distinct clades:

1. Amborella 2. Water Lilies 3. Star Anise & relatives 4. Magnoliids 5. Monocots 6. Eudicots

Water lilies, star anise and Amborella are minor

Water lily (Nymphaea Star anise (Illicium) angiosperm lineages that “Rene Gerard”) diverged from the rest of the angiosperms fairly early and collectively are referred to as basal angiosperms.

Amborella trichopoda Magnoliids

Magnoliids are more closely related to the monocots & eudicots than the 3 basal angiosperms.

• includes , laurels & black pepper plants

Southern (Magnolia grandiflora) Monocots vs Eudicots venation Stems

Monocot Characteristics

One Veins usually cotyledon parallel scattered

Eudicot Characteristics

Vascular tissue Two Veins usually usually arranged cotyledons netlike in ring Monocots vs Eudicots (cont’d) Pollen Flower s Monocot Characteristics

Root system Floral organs usually fibrous Pollen grain usually in (no main ) with one multiples opening of three

Eudicot Characteristics

Floral organs Taproot Pollen grain usually in (main root) with three multiples of usually present openings four or five Monocots

More than ¼ of angiosperm species are monocots, most of which are grasses, Orchid Pygmy date palm (Phoenix roebelenii) (Lemboglossum rossii) palms or orchids.

• much of the calories consumed by humans come from monocot grasses (e.g., corn, wheat & rice) Barley (Hordeum vulgare), a grass Eudicots More than 2/3 of angiosperm species are eudicots of which there is great variety. Snow pea (Pisum Dog rose (), a wild rose sativum), a legume • the largest group is the legumes which includes peas & beans • this also includes most fruit and non-conifer

Pyrenean (Quercus pyrenaica)